nation

Unfortunately, in most cases, nations are not groups of people under a government (if this were true they would be more properly termed nation-states). This has proven to be one of the main challenges of international relations over the last century.

A state is a legal, sovereign entity with a government and a political system irrespective of any national definitions (nations).

Long before the creation of the State of Israel in 1948, the Nation of Israel consisted of Jews separated geographically around the world, though united in identity.

Taltos' explanation is right on the money, but the example of Yugoslavia is a little confusing because many of the nations in greater Yugoslavia went on to get their own states. Also, I would not consider Kosovo a nation but rather a political unit dominated by members of a greater Albanian nation.

The book takes place on an island called "Nation", somewhere in (what we would call) the South Pacific. The island is considered significant and large by its inhabitants, although it seems to be no more than a few dozen square miles in area. The plot of the book involves a tsunami that wipes out almost all but one member of the Nation, as well as people on surrounding islands. The only survivor of the Nation is Mau, a boy who has just completed his manhood ritual on a distant island, and is in a canoe when the wave hits. Also on the island is a British naval ship, with only one survivor: Daphne, the daughter of the British governor of the area. Together, Daphne and Mau must quickly overcome the remaining natural hazards and cultural barriers if they are to survive in this world. Other survivors join them, and through a series of plot complications, different philosophical and cultural issues are brought up and then (such as it were) solved.

Although not a Discworld novel, the book explores many of the same themes that have been important in the later Discworld series: how people's individual needs, thoughts and decisions can be both constrained by, and build, a society. Also, compared to the Discworld novels, it tends to to be more somber in tone, having less word play and witticism, and more "realistic" dialog and description. It is still recognizably a Pratchett book, however.

Terry Pratchett's fans don't need a recommendation to read any of his books, but this book would actually be one of the first books I would recommend to get someone reading Pratchett, in part because the entire history of the Discworld is not needed to read it.